FORT HOOD, Texas — A Syrian insurgent held at Abu Ghraib prison testified by video Tuesday that Army Spc. Charles Graner merrily whistled, sang and laughed while brutalizing him and forced him to eat pork and drink alcohol in violation of his Muslim faith.

An Iraqi prisoner later told the court that he was among a group of prisoners stripped by Graner and other Abu Ghraib guards, stacked up naked in a human pyramid while female soldiers watched and later told to masturbate.

“I couldn’t imagine it in the beginning,” Hussein Mutar, the Iraqi, said when asked how he felt during the alleged mistreatment. “I could kill myself because no one over there was stopping it from happening.”

The prosecution rested after Mutar’s video testimony.

Defense begins Wednesday
The defense is scheduled to begin presenting Graner's case on Wednesday. His lawyers have maintained that Graner and other soldiers had no choice but to obey orders by military and civilian intelligence officers to soften up prisoners for questioning.

Amin al-Sheikh, the Syrian prisoner, testified that Graner threatened more than once to kill him and on one occasion told him to thank Jesus for keeping him alive.

The inmate also said he listened through his cell wall as Graner and other Americans forced a Yemeni prisoner to eat from a toilet.

Asked if Graner appeared to enjoy hurting him, al-Sheikh said through an interpreter: “He laughed. He was whistling. He was singing.”

He described Graner as the “primary torturer” and “a naturally aggressive man” — a characterization that led Graner, sitting in the courtroom, to roll his eyes and chuckle.

Graner is the first soldier accused in the Abu Ghraib scandal to go on trial. Prosecutors allege the Army reservist was the ringleader of the abuse. Three fellow guards from the 372nd Military Police Company have pleaded guilty to abusing prisoners.

Graner is charged with conspiracy, assault, committing indecent acts and other offenses. He could get to 17½ years in a military prison if found guilty by a jury of four Army officers and six enlisted men.

Inmate's assertionsAl-Sheikh said he went to Iraq in 2003 to fight U.S.-led forces, and he was taken to Abu Ghraib after being captured with AK-47 assault rifles, grenades and bomb-making material. While being held at a tent camp next to Abu Ghraib, al-Sheikh said, he was wounded in the leg and chest in a shootout with Americans after he obtained a handgun from an Iraqi guard.

Al-Sheikh said he was later sent to Abu Ghraib, where Graner jumped on his wounded leg and struck it with a collapsible metal stick. Another time, he said, Graner handcuffed him to his cell door with his arms behind his back for eight hours.

Graner also accompanied a U.S. soldier who urinated on him, and that the defendant was present when another American threatened to rape him, al-Sheikh said.

‘Steve’ and ‘Mikey’
Speaking outside court after the video testimony, Graner said he remembered al-Sheikh: “The last time I saw him, he was threatening to kill me.”

Under defense questioning, al-Sheikh said Graner at times worked with Americans who were interrogating him at Abu Ghraib. He said interrogators known as “Steve” and “Mikey” made it clear that he would be roughed up by Graner if he did not cooperate.

Defense attorney Guy Womack said al-Sheikh’s testimony was good for his client. “It was the face of the enemy,” Womack said. “It’s very clear that he hates America.”

Al-Sheikh conceded that he did not see Graner and others making the Yemeni prisoner eat from the toilet, but said it was clear that was happening from what he heard.

After the last prosecution witness, Womack, Graner's attorney, made motions to dismiss two of the charges against his client. The judge denied the motions.

NBC News' Al Henkel in Fort Hood, Texas, and The Associated Press contributed to this report.